System and Method for Supporting Multi-User Antenna Beamforming in a Cellular Network

ABSTRACT

The present invention is a method and system for supporting a beamforming antenna system in a multiple user mobile broadband communication network including a process for setting and adjusting the magnitude and phase of the signal to user equipment from each antenna. Namely, the present invention supports the communication of power signal values or levels to user equipment in a manner that keeps pace with the rapid variations of the power levels that occur in the dynamic scheduling of transmissions on the cell site. The present invention satisfies this need for an improved signal strength signaling to user equipment for the situation where multiple users are located on the cell site.

RELATED APPLICATION DATA

This application is related to Provisional Patent Application Ser. No.61/075,215 filed on Jun. 24, 2008, and priority is claimed for thisearlier filing under 35 U.S.C. §119(e). The Provisional PatentApplication is incorporated by reference into this utility patentapplication.

TECHNICAL FIELD OF THE INVENTION

The invention relates supporting the signal power variations on spatialbeams for multiple users within a cell segment.

BACKGROUND OF THE INVENTION

There is an increasing demand on mobile wireless operators to providevoice and high-speed data services, and at the same time, theseoperators want to support more users per basestation to reduce overallnetwork costs and make the services affordable to subscribers. As aresult, wireless systems that enable higher data rates and highercapacities are needed. The available spectrum for wireless services islimited, however, and the prior attempts to increase traffic within afixed bandwidth have increased interference in the system and degradedsignal quality.

Wireless communications networks are typically divided into cells, witheach of the cells further divided into cell sectors. A base station isprovided in each cell to enable wireless communications with mobilestations located within the cell. One problem exists when prior artomni-directional antennas are used at the basestation because thetransmission/reception of each user's signal becomes a source ofinterference to other users located in the same cell location on thenetwork, making the overall system interference limited. Such anomni-directional antenna is shown in FIG. 1( a).

In these traditional omni-directional antenna cellular network systems,the base station has no information on the position of the mobile unitswithin the cell and radiates the signal in all directions within thecell in order to provide radio coverage. This results in wasting poweron transmissions when there are no mobile units to reach, in addition tocausing interference for adjacent cells using the same frequency, socalled co-channel cells. Likewise, in reception, the antenna receivessignals coming from all directions including noise and interference.

An effective way to increase efficiency of bandwidth usage and reducethis type of interference is to use multiple input-multiple output(MIMO) technology that supports multiple antennas at the transmitter andreceiver. For a multiple antenna broadcast channel, such as the downlinkon a cellular network, transmit/receive strategies have been developedto maximize the downlink throughput by splitting up the cell intomultiple sectors and using sectorized antennas to simultaneouslycommunicate with multiple users. Such sectorized antenna technologyoffers a significantly improved solution to reduce interference levelsand improve the system capacity.

The sectorized antenna system is characterized by a centralizedtransmitter (cell site/tower) that simultaneously communicates withmultiple receivers (user equipment, cell phone, etc.) that are involvedin the communication session. With this technology, each user's signalis transmitted and received by the basestation only in the direction ofthat particular user. This allows the system to significantly reduce theoverall interference in the system. A sectorized antenna system, asshown in FIG. 1( b), consists of an array of antennas that directdifferent transmission/reception beams toward users located in thecoverage area of the sector of the cell.

To improve the performance of a sectorized cell sector, schemes havebeen implemented using orthogonal frequency domain multiple access(OFDMA) systems, which are also called Space-Division Multiple Access(SDMA) systems. In these systems, mobile stations can communicate withthe base station using one or more of these spatial beams. This methodof orthogonally directing transmissions and reception of signals, calledbeamforming, is made possible through advanced signal processing at thebase station.

A beamforming scheme is defined by the formation of multiple spatialbeams within a cell sector to divide the cell sector into differentcoverage areas. The radiation pattern of the base station, both intransmission and reception, is adapted to each user to obtain highestgain in the direction of that user. By using sectorized antennatechnology and by leveraging the spatial location and channelcharacteristics of mobile units within the cell, communicationtechniques called space-division multiple access (SDMA) have beendeveloped for enhancing performance. Space-Division Multiple Access(SDMA) techniques essentially creates multiple, uncorrelated spatialpipes transmitting simultaneously through beamforming and/or precoding,by which it is able to offer superior performance in multiple accessradio communication systems.

One type of beamforming scheme is an adaptive beamforming scheme thatdynamically directs beams toward a location of a mobile station. Such anadaptive beamforming scheme requires mobility tracking in whichlocations and spatial characteristics of mobile stations are tracked forthe purpose of producing the adaptive beams. Depending on location andspatial characteristics, each user's signal is multiplied by complexweightings that adjust the magnitude and phase of the signal to and fromeach antenna. This causes the output from the array of sectorizedantennas to form a transmit/receive beam in the desired direction andminimizes the output in other directions, which can be seen graphicallyin FIG. 2. Precoding is an implementation of beamforming that usespredetermined codewords, where each codeword is a set of weights for theantenna elements.

To support communications to the user equipment, the user equipment willbe instructed about the power signal values or signal levels that needto be set for transmissions to the user equipment, especially whenmultiple users are located on the cell site. In the prior art, the userequipment 205 and 210 is instructed as to the energy allocation perresource element (EPRE) power level by Radio Resource Control (RRC)signaling as shown in early releases of the 3GPP TS 36.213 standard.(e.g., TS 36.213 v8.3.0) But, due to the dynamic nature of scheduling,the RRC signaling of power levels has proven too slow to keep pace withthe rapid variations in the power level that are encountered on thesystem. This problem leads to performance loss because users on themultiple user-MIMO system can be changed at a higher rate than thefrequency of RRC signaling. Further, there are other disadvantages tousing the RRC signaling to designate power levels to the user equipment,including increased scheduler complexity and the need for more RRCsignaling of power levels.

Because the currently known methods of instructing the user equipmentabout the energy allocation per resource element (EPRE), which is thesignal strength value or level for transmissions to the user equipment,are not fast enough to keep pace with the rapid variations of powerlevels that occur in the dynamic scheduling of transmissions on the cellsite, there is a need for an improved signal strength or level signalingto user equipment, especially where multiple users that are located onthe same cell site can be scheduled for transmission using the samechannel resources. There is also a need for support of sectorizedbeamforming antenna systems in a multiple user mobile broadbandcommunication network, including solving the above-identified problem.

The various components on the system may be called different namesdepending on the nomenclature used on any particular networkconfiguration or communication system. For instance, “user equipment”encompasses PC's on a cabled network, as well as other types ofequipment coupled by wireless connectivity directly to the cellularnetwork as can be experienced by various makes and models of mobileterminals (“cell phones”) having various features and functionality,such as Internet access, e-mail, messaging services, and the like.

Further, the words “receiver” and “transmitter” may be referred to as“access point” (AP), “basestation,” and “user” depending on whichdirection the communication is being transmitted and received. Forexample, an access point AP or a basestation (eNodeB or eNB) is thetransmitter and a user is the receiver for downlink environments,whereas an access point AP or a basestaion (eNodeB or eNB) is thereceiver and a user is the transmitter for uplink environments. Theseterms (such as transmitter or receiver) are not meant to berestrictively defined, but could include various mobile communicationunits or transmission devices located on the network.

SUMMARY OF THE INVENTION

The present invention is a method and system for supporting abeamforming antenna system in a multiple user mobile broadbandcommunication network including a process for setting and adjusting themagnitude and phase of the signal to user equipment from each antenna.Namely, the present invention supports the communication of power signalvalues or levels to user equipment in a manner that keeps pace with therapid variations of the power levels that occur in the dynamicscheduling of transmissions on the cell site. The present inventionsatisfies this need for an improved signal strength signaling to userequipment for the situation where multiple users are located on the cellsite.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the invention will become more readilyunderstood from the following detailed description and appended claimswhen read in conjunction with the accompanying drawings in which likenumerals represent like elements and in which:

FIG. 1 is a graphical illustration of an omni-directional antenna (a)and a sectorized antenna (b);

FIG. 2 is a graphical illustration of a weighted sectorized transmissionbeam directed to the desired user; and,

FIG. 3 is a block diagram of exemplary components of a base station andmobile station.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1( a), the overall transmission architecture 100 of anomni-directional antenna 105 that transmits radially outward equally invarious directions shown by arrows 125, 115, 135 and 140. The perimeterof the coverage area is shown by the area 120 for the transmissionarchitecture 100. Improved efficiencies have been achieved by using thesectorized antenna architecture 141 shown in FIG. 1( b).

Multiple antennas 145, 147 and 148 are shown in the architecture 140,wherein each antenna is directed toward a different region of thecellular network shown by the directional transmission 175 for coveragearea 150, transmission 190 for coverage area 157, and directionaltransmission 180 for coverage area 155. In this context, it is possiblefor system capacity to be improved by the sectorized architecture.

By varying the strength of various transmission signals, additionalefficiencies and reduced interferences can be achieved as shown in FIG.2 for the sectorized architecture 200. Multiple antenna 215, 220, 227and 230 direct transmissions (or receive transmissions) in thesectorized antenna architecture 200. A directional antenna beam 235 isformed by increasing the strength of that signal from antenna element230. The desired user 205 is shown receiving a desired transmission 245in high signal strength coverage area 235, which is a higher poweredbeam meant to be directed to that user 205. An interfering user 210 isshown with lower strength transmission signal 240, which reduces theinterference encountered in the system related to that user 210.

In accordance with some preferred embodiments, an “opportunistic” spacetime multiple access (OSTMA) technique is provided for use in wirelesscommunications networks. The OSTMA technique enables the formation ofmultiple spatial beams in a cell segment (cell or cell sector), where atleast some of the multiple spatial beams of the cell segment areassociated with different power levels to provide different coverageareas within the cell segment. A spatial beam (or more simply “beam”)refers to a geographically distinct coverage region within a cellsegment in which wireless communication between a base station andmobile station(s) can be performed.

The OSTMA scheme is provided for the forward wireless link from the basestation to the mobile stations. In alternative embodiments, the OSTMAscheme can also be used for the reverse wireless link from the mobilestation to the base station. The communication connection in which dataflow from the base station to the mobile station is called the forwardlink (FL). Likewise, the communication connection in which data flowfrom the mobile station to the base station is called the reverse link(RL). Communication conditions are not always the same for both the FLand the RL. For example, a mobile station may be communicating with aserving base station which has a highly congestive RL traffic but arelatively open FL flow. The mobile station may need to adjust its RLconnections because to stay with the same base station for both FL andthe RL (if a more open RL connection is available from another basestation) may not be the best use of communication resources.

Exemplary components in the preferred embodiment include a base station1000 and mobile station 1002 are depicted in FIG. 3. The base station1000 includes a wireless interface 1004 to communicate wirelessly over awireless link with a wireless interface 1006 in the mobile station 1002.The base station 1000 includes software 1008 that is executable on oneor more central processing units (CPUs) 1010 in the base station 1000 toperform tasks of the base station. The CPU(s) 1010 is (are) connected toa memory 1012. The software 1008 can include a scheduler and othersoftware modules. The base station 1000 also includes an inter-basestation interface 1014 to communicate information with another basestation, such as backhaul information and/or coordination information.

Similarly, the mobile station 1002 includes software 1016 executable onone or more CPUs 1018 connected to a memory 1020. The software 1016 isexecutable to perform tasks of the mobile station 1002. Instructions ofsuch software (1008 and 1016) can be loaded for execution onto the CPUsor other types of processors. The processor can include amicroprocessor, microcontroller, processor module or subsystem(including one or more microprocessors or microcontrollers), or othercontrol or computing devices. A “processor” can refer to a singlecomponent or to plural components.

Data and instructions (of the software) are stored in respective storagedevices, which are implemented as one or more computer-readable orcomputer-usable storage media. The storage media include different formsof memory including semiconductor memory devices such as dynamic orstatic random access memories (DRAMs or SRAMs), erasable andprogrammable read-only memories (EPROMs), electrically erasable andprogrammable read-only memories (ERPROMs) and flash memories; magneticdisks such as fixed, floppy and removable disks; other magnetic mediaincluding tape; and optical media such as compact disks (CDs) or digitalvideo disks (DVDs).

When multiple users 205 and 210, such as shown on FIG. 2, are beingserviced on the same cell site sector, the signal power from thetransmission antenna 230 must be divided between those multiple users.User 205 or 210 in the multiple user-MIMO mode should expect that theirEPRE power level can take one of several values depending on the numberof multiple users simultaneously being serviced on that cell sitesector.

In the prior art, the user equipment 205 and 210 is instructed as to theEPRE power level by Radio Resource Control (RRC) signaling as shown inearly releases of the 3GPP TS 36.213 standard. (e.g., TS 36.213 v8.3.0)But, due to the dynamic nature of scheduling, the RRC signaling of powerlevels has proven too slow to keep pace with the rapid variations in thepower level that are encountered on the system. This problem leads toperformance loss because users on the multiple user-MIMO system can bechanged at a higher rate than the frequency of RRC signaling. Further,there are other disadvantages to using the RRC signaling to designatepower levels to the user equipment, including increased schedulercomplexity and the need for more RRC signaling of power levels.

The present invention solves the problem associated with RRC signalingof power levels by providing power level information to the userequipment 205 or 210 through bits designated in the scheduling messagefor users in the multiple user-MIMO mode. The advantages of using thescheduling message to communicate the power level information, asopposed to the RRC signaling, include full scheduler flexibility,improved performance and reduced need for RRC signaling for a scalingfactor update. Further, because the signal to noise ratio for multipleuser-MIMO users tends to be quite high, the increased control channeloverhead for including the power level information in the Grant message(as a percentage of the achievable throughput) will be quite small.

The present invention uses several bits in the scheduling messagetransmitted to users 205 and 210 (or mobile station 1002) from thebasestation 1000. The scheduling Grant message can be described as itrelates to the Physical Downlink Shared Channel (PDSCH) transmissionmodes identified in the signaling format for multiple user-MIMOtransmissions. The present invention merges the multiple user-MIMO andclosed-loop Rank-1 precoding transmission modes into a singledesignation mode with transmission antenna designation bits because theclosed loop precoding transmission mode is a subset of the multipleuser-MIMO mode. Namely, the invention allows for the dynamic switchingbetween the multiple user-MIMO and closed loop Rank-1 and Rank-2precoding transmissions through the designation bits in the schedulingmessage, without the need for higher layer RRC signaling that would benecessary in the prior art for changing from one transmission mode toanother. By using designation bits in the scheduling message transmittedto users, the present invention combines the two separate transmissionmode designations into a single transmission mode designation, whichreduces the overhead of control messages and simplifies the transmissionmode designations in the system.

In the present invention, when the eNodeB is transmitting to multipleuser equipment, such as 205 and 210 in FIG. 2, the eNodeB must dividethe power between the different user equipment. The amount of powerdivision depends on the number of user equipment that must be served onthe cell segment using the same channel resources. For instance, if twouser equipment are being serviced, the power division to user equipment205 would be designated by the precoding table [1 1 1 1]/sqrt (2) and touser equipment 210 would be designated by the precoding table [1 −1 1−1]/sqrt (2), where 1/sqrt(2) is used as a scaling factor for the twoprecoders that reduce the power signals being transmitted to therespective user equipment. If a four transmitter antenna system issupported by the eNodeB, the precoder may scale the power level to userequipment 205 using the precoding table [1 1 1 1]/sqrt(N), while theother signals to other user equipment would be reduced by a proportionalfactor designated by a predetermined precoding table assigned for thoseother user equipment, for N users that are scheduled for the samechannel resources.

In the present invention, the scaling factor is signaled to the userequipment using additional designation bits in a message sent to theuser equipment. In one embodiment, additional bits can be added to a newformat message (e.g. Format 1B) or designation bits can bere-interpreted from designation bits in an existing message format (e.g.Format 2 for users in a multiple user-MIMO Grant message). If only twotransmitters are required because there are 1 to 2 users on the cellsegment, only one additional designation bit in the format message willbe needed. If four transmitters are required because there are up tofour users on the cell segment, two additional designation bit in theformat message will be needed.

When the user equipment 205 receives the bit designations in the formatmessage, it calculates the scaling factor to be applied to the powerlevel for that user equipment based on the number of transmitterantennas and users specified by the designation bits. The power scalingfactors P_A and P_B can be determined by the user in that manner, andthe power scaling factor can be used by the receiver to demodulate thereceived signal. The system dynamically adjusts the power of thetransmission signal in a very rapid manner with the use of thedesignation bits, and the user uses the scaling factor to demodulate thesignal at the receiver. The user equipment may calculate the scalingfactor P_A and P_B using a predetermined scaling factor, such as −10 log₁₀N, N=1, 2 for a 2 transmitter antenna bit designation using one bit or−10 log ₁₀N, N=1, 2, 3, 4 for a 4 transmitter antenna bit designationusing two bits, or values from a precoding table. This embodiment can beused with the new format message (e.g. Format 1B) or designation bitscan be re-interpreted from designation bits in an existing messageformat (e.g. Format 2 for users in a multiple user-MIMO Grant message).Alternatively, the designation bits can be used to look up the scalingfactor from a pre-coding look-up table or other table resource on thesystem.

Alternatively, the bit designations in the format message may providethe actual scaling values, P_A and P_B, to the user equipment, whichwill use more bits than the prior designation method but will allow forfaster protocol processing by eliminating a calculation of the P_A andP_B scaling values by the user equipment. The actual value of P_A andP_B scaling values can be specified in the designation bits, orrepresentative of a predetermined factor defined by a table, orotherwise known in the system. For instance, the three bits designatingP_A may define dB values to be applied to the power on the signalstrength (e.g. dB=3, 2, 1, 0, −1, −2, −3, −6), the designation bits maydefine a table entry in a specified scaling table (e.g. three bitsdesignates entries on a scaling or precoding table), or the scalingfactors known to the system are specified by P_A=−10 log ₁₀N, N=1, 2 fora 2 transmitter antenna bit designation or P_A=−10 log ₁₀N, N=1, 2, 3, 4for a 4 transmitter antenna bit designation. The power scaling factorsP_A and P_B can be determined by the user in that manner, and the powerscaling factor can be used by the receiver to demodulate the receivedsignal. The system dynamically adjusts the power of the transmissionsignal in a very rapid manner with the use of the designation bits, andthe user uses the scaling factor to demodulate the signal at thereceiver. This embodiment can be used with the new format message (e.g.Format 1B) or designation bits can be re-interpreted from designationbits in an existing message format (e.g. Format 2 for users in amultiple user-MIMO Grant message).

In the foregoing description, numerous details are set forth to providean understanding of the present invention. However, it will beunderstood by those skilled in the art that the present invention may bepracticed without these details. While the invention has been disclosedwith respect to a limited number of embodiments, those skilled in theart will appreciate numerous modifications and variations therefrom. Itis intended that the appended claims cover such modifications andvariations as fall within the true spirit and scope of the invention.

1. A method for specifying a power scaling factor for a transmissionbeam from an access node to a receiver on a communication system thathas at least two spatial beams providing coverage in a cell sector, themethod comprising: determining the power scaling factor at the accessnode that should be used to apply to the transmission signal to one ofthe receivers, said power scaling factor is determined based on theresource allocation on the network and number of receivers that will becommunicated to over the same resources, preparing a designation bitformat message at the access node based on the power scaling factordetermined by the access node, transmitting said designation bit formatmessage periodically from an access node over one or more spatial beamtransmissions, said designation bit signal used by the receiver tocalculate the power scaling factor for said transmission beam to saidreceiver; and adjusting the power of the transmission signal dynamicallyto the receiver based on the power scaling factor, said transmissionsignal is demodulated at the receiver using the power scaling factorcalculated from the designation bit format message.
 2. The method ofclaim 1, wherein if two transmitters are required because there are 1 to2 users on the cell segment, the designation bit format message willneed one additional designation bit in the format message.
 3. The methodof claim 1, wherein if four transmitters are required because there areup to four users on the cell segment, the designation bit format messagewill need two additional designation bit in the format message.
 4. Themethod of claim 1, wherein the power scaling factor is calculated usinga formula −10 log ₁₀N, N=1, 2 for a 2 transmitter antenna bitdesignation using one bit in the format message.
 5. The method of claim1, wherein the power scaling factor is calculated using a formula −10log ₁₀N, N=1, 2, 3, 4 for a 4 transmitter antenna bit designation usingtwo bits in the format message.
 6. The method of claim 1, wherein thepower scaling factor is calculated using a value designation from atable of predetermined values in the system.
 7. A method for specifyinga power scaling factor for a transmission beam from an access node to areceiver on a communication system that has at least two spatial beamsproviding coverage in a cell sector, the method comprising: determiningthe power scaling factor at the access node that should be used to applyto the transmission signal to one of the receivers, said power scalingfactor is the value adjustment to the transmission beam based on theresource allocation on the network and number of receivers that will becommunicated to over the same resources, preparing a designation bitformat message at the access node based on the power scaling factordetermined by the access node, transmitting said designation bit formatmessage periodically from an access node over one or more spatial beamtransmissions, said designation bit signal specifying to the receiverthe actual value of the power scaling factor for said transmission beamto said receiver; and, adjusting the power of the transmission signaldynamically to the receiver based on the power scaling factor, saidtransmission signal is demodulated at the receiver using the powerscaling factor calculated from the designation bit format message. 8.The method of claim 7, wherein designation bit format message willspecify a dB rating to be applied to the transmission signal.
 9. Themethod of claim 7, wherein the designation bit format will specifyactual values from a table of predetermined values in the system. 10.The method of claim 7, wherein the designation bit format specifies theactual power scaling value using a formula −10 log ₁₀N, N=1, 2 for a 2transmitter antenna bit designation using one bit in the format message.11. The method of claim 7, wherein the power scaling factor iscalculated using a formula −10 log ₁₀N, N=2 1, 2, 3, 4 for a 4transmitter antenna bit designation using two bits in the formatmessage.
 12. A transmission system that specifies a power scaling factorfor a transmission beam from an access node to a receiver on acommunication system that has at least two spatial beams providingcoverage in a cell sector, the system comprising: an access node thathas a processor that determines the power scaling factor that should beapplied to a transmission beam to said receiver based on the resourceallocation on the network and the number of receivers that will becommunicated to over the same resources and prepares a designation bitformat message based on that power scaling factor, and a transmitterthat transmits a designation bit format message periodically over one ormore spatial beam transmissions, said designation bit format messageused by the receiver to calculate a power scaling factor for saidtransmission beam to a receiver; said access node adjusting the power ofthe transmission signal dynamically to the receiver based on the powerscaling factor without creating interference with other transmissions onthe network, said transmission signal being demodulated at the receiverusing the power scaling factor received from the access node.
 13. Thesystem of claim 12, wherein if two transmitters are required becausethere are 1 to 2 users on the cell segment, the designation bit formatmessage will need one additional designation bit in the format message.14. The system of claim 12, wherein if four transmitters are requiredbecause there are up to four users on the cell segment, the designationbit format message will need two additional designation bit in theformat message.
 15. The system of claim 12, wherein the power scalingfactor is calculated using a formula −10 log ₁₀N, N=1, 2 for a 2transmitter antenna bit designation using one bit in the format message.16. The system of claim 12, wherein the power scaling factor iscalculated using a formula −10 log ₁₀N, N=1, 2, 3, 4 for a 4 transmitterantenna bit designation using two bits in the format message.
 17. Thesystem of claim 12, wherein the power scaling factor is calculated usinga value designation from a table of predetermined values in the system.18. A transmission system that specifies a power scaling factor for atransmission beam from an access node to a receiver on a communicationsystem that has at least two spatial beams providing coverage in a cellsector, the system comprising: an access node that has a processor thatdetermines the power scaling factor that is actual value adjustment beapplied to a transmission beam to said receiver based on the resourceallocation on the network and the number of receivers that will becommunicated to over the same resources, prepares a designation bitformat message based on that power scaling factor, and a transmittertransmits a designation bit format message periodically over one or morespatial beam transmissions, said designation bit format messagespecifying the actual value of the a power scaling factor to thereceiver for said transmission beam to a receiver; said access nodeadjusting the power of the transmission signal dynamically to thereceiver based on the power scaling factor without creating interferencewith other transmissions on the network, said transmission signal beingdemodulated at the receiver using the power scaling factor received fromthe access node.
 19. The system of claim 16, wherein designation bitformat message will specify a dB rating to be applied to thetransmission signal.
 20. The system of claim 16, wherein the designationbit format will specify actual value from a table of predeterminedvalues in the system.
 21. The system of claim 16, wherein thedesignation bit format specifies the actual power scaling value using aformula −10 log ₁₀N, N=1, 2 for a 2 transmitter antenna bit designationusing one bit in the format message.
 22. The system of claim 16, whereinthe power scaling factor is calculated using a formula −10 log ₁₀N, N=1,2, 3, 4 for a 4 transmitter antenna bit designation using two bits inthe format message.